1940 Wiper control knob

[50flathead]

Anybody know where to source the special nut that goes with this part?

 

[Kube]

Anybody know where to source the special nut that goes with this part?

Hardware store. It (the nut) is not all that special. Look in the lamp repair section. You know, the small tray boxes with special fittings, etc.

 

[19Fordy]

50flathead: If you decide to buy a complete new assembly look here:
https://www.dennis-carpenter.com/cars/exterior/windshield-wipers/01a-17535-b-wiper-onoff-switch